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The prospect of ruinous legal bills “can decrease the incentives for these firms to innovate,” the study found. “Innovators deciding to invest in new technology have to consider the risk of inadvertent infringement as a cost of doing business.”

Kodak, the once-dominant film company, in January filed a series of lawsuits against Samsung, Apple and HTC, as it headed into bankruptcy. The lawsuits accuse the companies of infringing on Kodak’s image-transmission technology, particularly in the case of Apple’s iPhone, iPad and iPod.

Some analysts say the most valuable asset left for Kodak, which failed to meet the challenges of foreign competition and the switch to digital photography, is its hoard of patents and the potential for payoffs in court if its lawsuits succeed.

Big tech-industry players, many with a deep inventory of patents, have tended to shy away from attacking one another, in a standoff many compared to the old Cold War nuclear detente. Going after a big rival for patent infringement could leave one vulnerable to a massive legal retaliatory strike.

But cases such as the Yahoo-Facebook and the Kodak filings suggest the old fears are breaking down.

Many active patent plaintiffs are essentially in the licensing business, acquiring patents for products or technology that they never produce. Instead, they seek to sell the rights to other companies.

Such is the case with Varia Holdings, which sued Samsung and Research in Motion, the maker of BlackBerry, last week for allegedly infringing on its patent for the use of “emoticons” on mobile phones and other mobile devices. In another example, Purple Leaf in July sued Amazon, Google and PayPal over a patent related to electronic checkout services.

Eolas Technologies, a company that won a $521 million patent-infringement award from a jury against Microsoft in 2003 (later overturned on appeal) is now in a Texas court contending it essentially owns the rights to many interactive features of the Web, including the function that offers a “search suggestion” when you’re entering a term in the search bar.

‘Fuzzy patents’

Fueling the rush to the courthouse is the uncertainty over what can and cannot be protected under patent law.

Plaintiffs thrive on “fuzzy patents,” which they can use to claim ownership of popular technologies, according to the BU study. “They buy up vaguely worded patents that can be construed to cover established technologies and use them opportunistically to extract licensing fees from the real innovators.”

But some say the overall health and growth of the industry indicate that the fears are overblown.

“If it was going to ruin the industry, it would have happened a decade or two ago,” said Jeff Kagan, a wireless and telecommunications industry analyst based in Atlanta.

Mr. Kagan said patent litigation has been heating up in part because it’s hard to keep up with technology’s ever-changing pace.

“Technology has been exploding,” he said. “It’s so far ahead of our ability to keep track of it. Eventually, when we catch up, we find things that are wrong, and lawsuits are filed.”